Shifting hard

I have a 1998 gmc 1500 2wd and my trans shifts hard after driving for a while but if i stop and turn the truck off and let it sit for 10-15 minutes and get back in it it shifts fine. Then does it again when the fluid thins out.

I had to replace intake manifold gaskets, did not realize, I broke coolant sensor, on test drive experienced hard shifting.
By chance I thought may the coolant sensor had something to do with the pro...

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